Industrial automated plants need input or output devices connected to them in order to be able to be operated; this is known as process interfacing. Output devices or, in other words, monitoring devices are, for example, control lamps and alphanumeric or graphic displays which inform the plant operator about the current state of the plant. Input devices or, in other words, operator devices are e.g. switches, rotary knobs or keyboards for alphanumeric inputting, which enable the operator to interfere with the plant.